Analysis of parallel BVI: experiences at CIRA

Blade-vortex interactions (BVI) occur in helicopter rotors when a rotor blade passes in the vicinity or through a tip vortex trailing from the same or the preceding blade. It is commonly accepted that parallel interactions, due to their highly unsteady 2D nature, are an ideal model problem for developing general 3D methodologies. Three different methodologies have been adapted and applied at CIRA to the analysis of the parallel BVI problem. The results have been compared on a classical test case. Morino's Boundary Integral Equation Method (BIEM) and a Velocity based Panel Method (VPM) have been applied to the analysis of incompressible BVI providing results that are in a satisfactory agreement amongst them. A transpiration velocity approach has been applied to a 2D Finite Difference Method (FDM) for compressible BVI. The results have been compared with BIEM and other methods proposed in literature. A reasonable agreement has been generally found for low Mach numbers (M_infty=0.3)